This invention relates to an image forming apparatus such as an electrophotographic apparatus, and particularly to a technology for preventing the leakage of a toner from a developing device of the image forming apparatus.
Generally, a developing device used in an image forming apparatus (for example, an electrophotographic apparatus) includes a developing roller that supplies a toner to a photosensitive drum, and a supply roller that supplies the toner stored in a toner storing portion to the developing roller. In order to prevent the toner moving outward in the axial direction of the developing roller from leaking out of the developing device, seal members are fixed to a casing of the developing device. The seal members slidably contact a circumferential surface of both ends of the developing roller. If the contact area between the seal members and the circumferential surface of the developing roller is increased, the effect of preventing the leakage of the toner is enhanced. However, in such a case, the friction between the seal members and the circumferential surface of the developing roller may increase, and therefore a load torque of a motor for driving the developing roller may also increase. As a result, the motor may become larger, and the abrasive wear may increase.
In order to solve this problem, it is proposed to form a hole or a cutout portion on each seal member 102 as shown in FIG. 10 (for example, Japanese Laid-open Patent Publication No. 7-333988: Patent Document 1). The hole or cutout portion is formed on the upstream side of each seal member 102 along the rotational direction of the developing roller 101. The contact area between the seal member 102 and the circumferential surface of the developing roller 101 is larger on the downstream side than on the upstream side, so that a large sealing effect is obtained on the downstream side of the seal member 102. With such a structure, a large sealing effect can be partially obtained, and the whole contact area between the seal member 102 and the circumferential surface of the developing roller 101 can be small.
Moreover, it is also proposed to provide separate seal members 103 and 104 respectively on the upstream side and on the downstream side along the rotational direction of the developing roller 101 as shown in FIG. 11 (for example, Japanese Laid-open Patent Publication No. 11-338253: Patent Document 2). The toner adhering to the circumferential surface of the developing roller 101 between the seal members 103 and 104 may freely falls from the circumferential surface of the developing roller 101, and the toner having reached the seal member 104 may be scraped off by the seal member 104. The whole contact area between the seal members 103 and 104 and the circumferential surface of the developing roller 101 can be small.
However, the seal member 102 (FIG. 10) disclosed in Patent Document 1 may be breakable because the seal member 102 has the hole or the cutout portion. In addition, the seal member 102 is bonded to a casing of the developing device with a small bonding area, and therefore the seal member 102 may easily be separated from the casing of the developing device.
Moreover, it is also proposed to provide separate seal members 103 and 104 respectively on the upstream side and on the downstream side along the rotational direction of the developing roller 101 as shown in FIG. 11 (for example, Japanese Laid-open Patent Publication No. 11-338253: Patent Document 2). The toner adhering to the circumferential surface of the developing roller 101 between the seal members 103 and 104 may freely fall from the circumferential surface of the developing roller 101, and the toner having reached the seal member 104 may be scraped off by the seal member 104. The whole contact area between the seal members 103 and 104 and the circumferential surface of the developing roller 101 can be small.